In order to increase the degree of integration of semiconductor devices, some means such as the formation of more minute patterns, and the production of multilayered circuits are now being devised. As one of these means, there is a technology in which wiring layers are formed as multiple layers. In order to attain multi-layer interconnection structure, an wiring layer of layer number n and that of layer number (n+1) are connected by a conductive layer, and, at the same time, a thin film called interlayer dielectric film is formed in the region other than the conductive layer.
SiO.sub.2 film has been known as a representative of this interlayer dielectric film. In recent years, however, it is required to decrease the relative dielectric constant of the interlayer dielectric film in order to further increase the speed of device operation, and studies are now being made on materials suitable for the interlayer dielectric film. Namely, the relative dielectric constant of SiO.sub.2 is approximately "4", and energy is now being directed to the investigation of materials whose relative dielectric constants are lower than this value. As one of such materials, SiOF whose relative dielectric constant is "3.5" is now being tried to put into practical use. However, we are paying attention to fluorocarbon film whose relative dielectric constant is lower than this.
The interlayer dielectric film is required to have not only a low relative dielectric constant but also high adhesion, high mechanical strength, excellent thermal stability and the like. Teflon (trade name) (polytetrafluoroethylene) is well known as fluorocarbon. However, this one is extremely poor in adhesion, and also has low hardness. Therefore, even if it is tried to use fluorocarbon film as the interlayer dielectric film, there are many unknown points regarding the quality of the film, and it is difficult to put fluorocarbon film into practical use under the present conditions.